window.onload = function(){
    var box = document.querySelector('.box');
    var img = box.querySelectorAll('img');
    // console.log(img.length);
    for(var i = 0;i<img.length;i++){
        //onmouseover 鼠标滑动
        img[i].onmouseover = function (){
            document.body.style.backgroundImage = 'url('+this.src+')';
        }
    }
}